This invention relates to a silencer for an outboard engine and more particularly to an improved air inlet device for a machine and a method for forming such an air inlet device.
Many forms of machines induct air and it is a common practice to employ some form of air silencer device for directing atmospheric air to the machine and for silencing the inducted air. Although these purposes are generally straight forward and clear, the spacial limitations frequently make it difficult to form a low cost yet highly effective silencer for such applications. The problems attendant with the designing of such a silencer may be best understood by reference to FIG. 1 which is a top plan view of a power head, indicated generally by the reference numeral 11, of an outboard motor. The power head 11 includes an internal combustion engine, indicated generally by the reference numeral 12 that is contained within a surrounding protective cowling, shown in phantom, and identified by the reference numeral 13. In the illustrated example, the engine 12 is of the V type and has angularly disposed cylinder banks 14 in which pistons 15 reciprocate. The pistons 15 are connected by means of connecting rods 16 to a crankshaft 17 that rotates about a generally vertically disposed axis. Because of the application of the engine 12 to an outboard motor, the crankshaft normally rotates about such a vertical axis.
The engine 12 is of the two cycle, crankcase compression type and for that reason is provided with one or more carburetors 18 that deliver a fuel/air mixture to the individual sealed crankcase chambers of the engine 12. An air inlet silencing device 19 is affixed to the carburetors 18 and draws air from within the protection cowling 13 for delivery to the carburetors 18. As may be readily seen from FIG. 1, the configuration of the engine and its protective cowling 13 dictates a relatively small size for the air inlet silencing device 19.
Referring now additionally to FIG. 2, a conventional form of air inlet silencing device 19 is shown in horizonal cross-section. The air inlet device 19 is normally made up of two parts 21 and 22 which may be conveniently formed from a molded plastic with the parts being formed in a permanent mold. The parts 21 and 22 are affixed to each other along a common face 23 as by bonding, welding or the like.
The air inlet device 19 defines an internal plenum chamber 24 to which air is admitted by means of pairs of rearwardly facing diverging air inlets 25. The air inlets 25 terminate in atmospheric air inlet openings 26 that are defined by perforated walls formed in the body portion 21. It should be readily apparent that the effective area of the inlet openings 26 should be substantially large so as to provide adequate air flow to the carburetors 18 and engine 12. Previously proposed constructions have, however, provided relatively restricted air inlet openings 26 for the reason now to be described.
As has been noted, the air inlet device portions 21 and 22 are normally formed from a plastic by a molding process. This is normally done in a permanent mold that is comprised of two parts and which parts move together and away from each other. In their closed position, they define a cavity into which fluid material is introduced so as to fill this cavity and form the body of the resultant part 21 or 22.
Turning specifically to the formation of the part 21, the two mold parts have mating faces that meet along a plane A and which move in their opened and closed directions in the perpendicular directions B and C. As such, the inlet channels 25 are formed with a configuration wherein the inner walls thereof must accommodate this perpendicular movement. As a result, the outer wall surfaces of the part 21 are relatively thick, as at 27, so as to provide a straight surface 28 that will accommodate the mold movement along the direction B. As a result, the inlet channels 25 rather than being of a uniform cross-sectional configuration have a reduced area at their inlet end that will restrict flow into the plenum chamber 24.
It is, therefore, a principal object of this invention to provide an air inlet device for a machine that will not restrict inlet flow and yet which can be conveniently formed in a permanent mold.
It is a further object of this invention to provide an air inlet device for an engine or the like which will permit adequate air flow and which can be easily formed in a permanent mold.
It is another object of this invention to provide an air inlet device for a machine in which the flow inlet area is substantially unrestricted but nevertheless compact.